1. Field of the Invention
The present invention relates to a nonaqueous cleaning liquid that is suitably used in a method for etching processing of a silicon substrate by the BOSCH method, and a method for processing a silicon substrate using the nonaqueous cleaning liquid.
2. Related Art
In, for example, a process for processing a MEMS (Micro Electro Mechanical System), a process for processing a through-silicon via (TSV), and the like, it may be necessary to deeply excavate a silicon substrate by etching. In this case, an etching process called the BOSCH method is often employed because it is easy to control the etching rate and the aspect ratio of the hole formed by etching.
The BOSCH method is a method for progressively excavating a silicon substrate while forming a fluorocarbon layer with a fluorocarbon gas on the inner surface of a portion excavated by etching. Accordingly, a fluorocarbon layer is deposited on the inner surface of the hole formed in the silicon substrate. Therefore, when the hole is formed in a silicon substrate by the BOSCH method, it is necessary to eventually remove the fluorocarbon layer deposited on the inner surface of the hole.
Thus, several methods have been proposed for removing the fluorocarbon layer deposited on the inner surface of the hole formed by the BOSCH method. Examples of the specific method include a method in which the fluorocarbon layer is cleaned off using ethyl perfluorobutyl ether (HFE-7200, manufactured by Sumitomo 3M Limited) as a special chemical liquid (Non-Patent Document 1) and a method in which the fluorocarbon layer is cleaned off with a mixed liquid of aqueous hydrogen peroxide, a basic chemical liquid such as tetramethylammonium hydroxide and water (Patent Document 1).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2012-023339    Non-Patent Document 1: Masaki Esashi, “Electronic Journal, 98th Technical Seminar, Foundation and Application of MEMS, Through Explanation”, pages 44 to 45, [online], Electronic Journal Co., [Search Jun. 13, 2012], Internet (URL: http://www.electronicjournal.co.jp/pdf/t_seminer/t098/01.pdf)